The present invention relates to a cutting plate for a ball race milling cutter and to an appropriate ball race milling cutter per se. In particular, such a cutting plate is provided with an upper and a lower surface that are substantially parallel to one another, wherein circumferential (continuous) edge surfaces connect the upper surface and the lower surface to one another, and wherein cutting edges are configured at least in part along the lines of intersection between the edge surfaces and the upper and/or lower surfaces. The feature that the upper and the lower surface are substantially parallel to one another clearly does not exclude deviation from parallel configuration or contouring with chip-guiding and chip-breaking structures.
The present invention also relates to a corresponding ball race milling cutter that is provided with a shank, a cutting head and a milling cutter axis, wherein at the forward free end of the cutting head there is provided at least one seat for an appropriate cutting plate.
Lastly, the present invention also relates to a method for manufacturing ball races with the aid of ball race milling cutters equipped with cutting plates, wherein active main and auxiliary cutting edges of the cutting plates are engaged respectively.
Corresponding ball race milling cutters and associated cutting plates have been known for a long time in the prior art, and are used in order to manufacture so-called ball races by cutting at a camber angle xcex1, that is to say grooves with a round, but nevertheless generally not exactly circular cross-section. The groove cross-section is instead configured such that the radius of curvature at the base of the groove is smaller than the radius of the balls that will roll along this race. The depth of this groove is also generally less than the radius of the balls, wherein in cross-section, the lateral flanks of the groove have a radius of curvature that is somewhat greater than the radius of the balls rolling along it, so the balls rolling in the ball race substantially touch only the flank areas of the ball race and engage neither with the base of the groove nor with the upper edges of the groove. This makes possible a very exactly defined position for the balls at the same time as low rolling resistance, so by means of such ball races, different machine parts can be connected that have to move easily against one another, even when they are relatively heavy and/or large amounts of force have to be transmitted between these machine parts (and via the balls lying in between them). Ideally, the cross-section of the ball race is substantially elliptical with an eccentricity of 1.01 to 1.1, and a large semi-axis symmetrically dividing the ball race, wherein the small semi-axis is slightly larger than the radius of the balls that will roll in the race, and the eccentricity is matched to the radius of the balls such that the points of contact of the balls on the race, seen from the cross-section of the balls, lie approximately 70xc2x0 to 90xc2x0 apart, that is on the flanks of the ball race at approximately 35xc2x0 to 45xc2x0 from the base thereof.
FIG. 1 shows by way of an example a cross-section through a so-called pivot pin in the form of a more or less cylindrical bush on the internal surface of which there are several ball races axially or slightly inclined towards the axis, which in cross-section appear approximately the shape of a segment of a circle.
FIG. 2 shows in an enlarged detail view that the cross-section of the corresponding ball race is not circular, but instead elliptical, and is substantially characterised by a radius of curvature at the base of the ball race that is somewhat smaller than the radius of the balls, and by a radius of curvature in the flank area of the groove or respectively the ball race, that is larger than the radius of the balls. In the upper area, the groove width generally exceeds the ball diameter, at least the diameter of the ball at the height of the groove edges.
Corresponding ball races are, as already described, produced in the prior art with special ball race milling cutters that are arranged at a so-called camber angle xcex1 to the surface of the work piece, and in the end face area of which at least one specially formed cutting plate is located with which the desired groove shape is milled. The so-called camber angle is the angle between the milling cutter axis and the axis of the ball race or respectively the tangent on the axis in the section of the ball race that is currently being worked. Such a camber angle is typically in the range between 10xc2x0 and 40xc2x0.
The cutting plates that are used in the end face area of the milling cutter generally have a shape that is approximately circular, sometimes slightly flattened in plan view, or more or less oval. They cut both with a main cutting edge arranged on the end face of the milling cutter, that has a directional component both in the axial direction as well as in a plane perpendicular to the milling cutter axis, and an auxiliary cutting edge that has a directional component more strongly parallel to the axis of the milling cutter. When using oval or respectively approximately circular cutting plates, the main and auxiliary cutting edges are obviously rounded and the transition from the main cutting edge to the auxiliary cutting edges is practically continuous without there being a clear differentiation between main and auxiliary cutting edges. Generally, however, this prior art can be characterised in that in the cutting edge section referred to as the xe2x80x9cmain cutting edgexe2x80x9d, the radial component of the cutting edge predominates, whereas the auxiliary cutting edge is defined by a stronger axial component.
The setting of the milling cutter axis in the camber angle, described hereinabove, with respect to the surface of the work piece is implemented in that the base of the groove is cut by a part or respectively a section of the cutting edge of the cutting plate that lies relatively far forward in the axial direction, and is at a shorter distance from the axis of the milling cutter than parts of the auxiliary cutting edge set further back axially. This means that the base of the groove is formed by a cutting edge section rotating on a smaller orbit, and thereby a smaller radius of curvature (if additionally dependent on the camber angle) than the flank sections of the groove or respectively the ball race that are cut by the auxiliary cutting edge areas that are further to the rear axially and further away radially from the axis of the milling cutter, that, because of the inclined adjustment of the milling cutter with respect to the surface of the work piece, cannot however reach the base of the groove.
The result is the at least approximately elliptical cross-sectional shape of the groove shown in principle in FIG. 2.
A disadvantage of the known cutting plates and ball race milling cutters is nevertheless in that for each ball diameter that necessitates a correspondingly dimensioned ball race, a cutting plate or respectively a cutting plate matched solely to the corresponding ball race has to be used with a milling cutter that has the appropriate diameter. As corresponding ball bearings or respectively ball joints are used and designed with widely differing diameters of balls, that are typically between 10 and 30 mm, a large number of different cutting plates have to be stocked in order to be able to correctly mill the proper ball race for every ball diameter. This means that the cutting plates for each individual ball diameter are used in comparatively small numbers, and nevertheless the manufacturer of such ball races must stock a large number of such cutting plates in order to be able to produce any desired dimension of ball race. In this way both the individual cutting plates and the manufacturing of such ball races are very expensive.
With respect to this prior art, the object of the present invention is to provide a cutting plate and a corresponding ball race milling cutter that make it possible to produce ball races for different ball diameters with one and the same type of cutting plate, also even with different milling cutter diameters.
Furthermore, the present invention should make it possible for a ball race to be created with several cutting edges that are located on different indexable cutting plates.
With respect to the cutting plate, this object is solved in that the cutting plate is provided with a main cutting edge substantially to be arranged on the end face, and an auxiliary cutting edge, with an angle cutting edge at the transition between the main and auxiliary cutting edges, which angle cutting edge, in plan view on the upper surface, is rounded with a comparatively small radius for the angle cutting edge, whereby in the same plan view, the auxiliary cutting edge also has a radius of curvature that is clearly larger than the radius of the angle cutting edge, and that is on the other hand smaller than twice the milling cutter diameter for which the cutting plate is provided.
The course of the main cutting edge is therefore not of paramount importance, in general the main cutting edge is substantially in a radial direction, that is to say mainly in a plane perpendicular to the axis of the milling cutter. The angle area, or respectively the angle cutting edge has a comparatively small radius and, in contrast to the angle cutting edge, the auxiliary cutting edge has an obvious axial component and is radially further outwards, but for its part is, however, curved, and is at least mainly slightly inclined towards the axis of the milling cutter. This results in the angle area, namely the angle cutting edge, being clearly offset radially inwards compared to the parts of the auxiliary cutting edge lying radially furthest out and further to the rear axially, and at the same time is arranged in the frontmost end face area of the milling cutter or respectively of the cutting plate. With appropriate adjustment of the axis of the milling cutter in the camber angle described hereinabove, this means that the base of the groove is cut by the angle area or respectively the angle cutting edge, while the flanks of the groove or respectively the ball race flanks, are cut by the auxiliary cutting edge offset further to the rear axially and radially further outwards. The curvature thereof ensures that the flank sections obtain the desired curvature that in addition is also dependent upon the milling cutter radius and the camber angle.
Using the indexable cutting plate according to the invention, it is possible to fit milling cutters in a larger range of diameters, for example, with a milling cutter diameter between 12 and 18 mm, with one and the same cutting plate in order to manufacture ball races for correspondingly different ball diameters in the same order of size of 12 to 18 mm. In order to cover the standard diameter range of 12 to, for example, 27 mm, only two different cutting plates are therefore necessary, the radii of curvature of which, on the angle cutting edges and the auxiliary cutting edges, are matched appropriately.
The manufacturing and stocking costs of the special cutting plates for ball race milling cutters can be significantly reduced in this way. Further, the shape of the cutting plate allows the easy attachment of a plurality of cutting inserts onto one tool, preferably of two or three cutting plates at the same or approximately the same angular distances apart. Intentionally provided small deviations from the same angular distances produce resonance-free and possibly quieter running of the tool.
Embodiments of the invention are preferred in which the angle area merges respectively tangentially into the corresponding auxiliary cutting edges and also into the main cutting edges.
An embodiment of the invention is particularly preferred in which the transition of the angle radius into the auxiliary cutting edge radius is at an angle of transition or respectively a connecting angle xcfx84 that is smaller than the camber angle xcex1, wherein the connecting angle xcfx84 is defined by the angle formed by the tangents on the cutting edge in this point of transition with the imaginary axis of the milling cutter in the pre-determined state of installation of the cutting plate. In this way it is ensured that the base of the groove is actually cut by the angle area with the smaller radius, while the auxiliary cutting edge, that for its part is round, cuts the flank areas.
A connecting angle is preferred in the range between 10xc2x0 and 25xc2x0, while the camber angle xcex1 can be, for example, in the range of 12xc2x0 to 45xc2x0. In general, the connecting angle xcfx84 is preferably between 2xc2x0 and 12xc2x0 less than the camber angle, wherein the small differential value is preferably taken into account with smaller camber angles.
The radius of the angle cutting edge is preferably between 0.2 and 5 mm, and in particular between 0.4 and 2.4 mm. On the other hand, the radius of the auxiliary cutting edge is clearly larger and in the preferred embodiment of the invention is between 5 and 30 mm, in particular between 8 and 25 mm, whereby this radius is nevertheless also dependent upon the diameter of the milling cutter. Advantageously, the radius of the auxiliary cutting edge is therefore determined dependent upon the milling cutter diameter for which the cutting plate is provided, and in this case, the auxiliary cutting edge radius should be between 0.7 times and 0.95 times the diameter of the milling cutter, which means, the other way around, that for a given cutting plate with a given auxiliary cutting edge radius, the diameter of the milling cutter can correspondingly vary in order to satisfy the criterion described hereinabove, wherein the slight exceeding or falling short of this relationship can easily be tolerated.
The cutting plates can have, for example, a rectangular or selectively also a triangular basic shape, as is known in the prior art, wherein the term xe2x80x9ctriangularxe2x80x9d in this case also includes the so-called trigonal shape, while the term xe2x80x9crectangularxe2x80x9d also covers rhombic plates. It is simply of importance that one of the triangular or rectangular sides can find application as an end face main cutting edge, and can be arranged such that the auxiliary cutting edge connects with the angle cutting edge at the connecting angle described, and also has the curvature described hereinabove.
The configuration of the cutting plate as an indexable cutting plate is particularly preferred, so that once a cutting edge becomes worn, another cutting edge can be put into use. In the case of rectangular indexable cutting plates, such a plate has on its upper side, preferably in the diagonally opposite corner areas, the transition between the main cutting edge and auxiliary cutting edge, so on the upper side two main cutting edges and two auxiliary cutting edges lie diagonally opposite one another with an angle cutting edge lying between them.
With such rectangular indexable cutting plates, nevertheless, the underside of the plate can also be provided with cutting edges, preferably in exactly the same way as on the upper side, but on the remaining diagonal corners.
The ball race milling cutter is characterised by an appropriate plate seat for the plates presently described. Preferably, the ball race milling cutter according to the invention is provided with a plurality of seats for appropriate plates, at the same or approximately the same angular distances apart along its front periphery section.
With respect to the method described in the introduction for manufacturing ball races, the object that forms the basis of the invention is solved by the use of one or more cutting plates, wherein main and auxiliary cutting edges are separated by an angle cutting edge, the radius of which is between 0.2 and 5 mm, preferably between 0.4 and 2.5 mm, while the radius of curvature of the main and auxiliary cutting edges respectively is at least five times this, preferably more than ten times the radius of curvature of the angle cutter.
In the preferred embodiment of the method according to the invention the main cutting edge is substantially straight, which corresponds to a very large or respectively infinitely large radius of curvature, and in the radial direction, while the radius of curvature of the auxiliary cutting edge is in the range between half and twice the milling cutter radius (maximum half-measurement of the ball race). Moreover, using the method according to the invention the cutting plates have all the features defined in the claims.
To the extent that in the description hereinabove and the claims there are described cutting edges or cutting edge sections curved in a radius, it is clear that these do not absolutely have to have a constant radius of curvature, but this radius can also vary in the course of the respective sections within the framework of the limits disclosed in the claims or can also be replaced with a polygon of sections shorter, straighter and angled with respect to one another, when in the centre, beyond the section concerned, average curvatures are produced that fall within the ranges claimed.